1. Field of the Invention
The invention relates to a hydraulic vehicle brake system.
2. Description of the Prior Art
Such vehicle brake systems are conventional per se in motor vehicles. They have a master cylinder, which is actuated by muscle force by a vehicle driver by means of a brake pedal, or in the case of a motorcycle, by means of a manual brake lever. Wheel brake cylinders are connected hydraulically to the master cylinder. For antilock vehicle brake systems, brake pressure buildup valves and brake pressure reduction valves for modulating the brake pressure are disposed between the master cylinder and the wheel brake cylinders; for individual-wheel brake pressure modulation, one brake pressure buildup valve and one brake pressure reduction valve are disposed respectively upstream and downstream of each wheel brake cylinder. In simplified regulating systems, one brake pressure buildup valve and one brake pressure reduction valve can for instance be provided for the wheel brakes of one axle as well. Moreover, typically in each brake circuit is one hydraulic pump as a return pump and/or for pressure buildup, and a hydraulic reservoir as well as further hydraulic valves are provided. Such brake pressure regulating systems are known per se to one skilled in the art and will not be described further here, since they do not form the actual subject of the invention.
In motor vehicles, underpressure brake boosters are typical, for enhancing the muscle force of the diver of the vehicle. Electrohydraulic brake boosters and external-force brake systems are also known, in both of which an external power supply to the vehicle brake system is accomplished with a hydraulic pump that is driven by an electric motor. Temporary storage of brake fluid under pressure in a hydraulic reservoir is typical. In the event of brake boosting, or in other words a so-called auxiliary force brake system, the brake pressure generated by the driver by muscle force by actuation of the master cylinder is enhanced with the external power supply; in the case of an external force brake system, the pressure buildup is effected solely with the external power supply; the master cylinder is disconnected hydraulically from the rest of the vehicle brake system. Only upon auxiliary braking, or in other words emergency braking in the event of failure of the external power supply is the actuation effected by muscle force using the master cylinder.